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Screw thread fastening system is the category of mechanical connection utilizing both wedge and friction actions to transfer clamping force and torque. This fastening system shows the advantages of simple in structure and ease in application. However, its shortcomings include the performance limitation by dimension and precision, stress concentration induced by the notch geometry, loosening in dynamical service, susceptible to atmospheric condition, etc. Therefore, the possible interference on the anti-loosening property of the locknut by noise factors of the ambient temperature, operator characteristics, and type of torque wrench used was investigated using Taguchi method in this study beside the main control factors of type of locknut, fit clearance, and type of lubrication grease. The goal was to evaluate the anti-loosening property of the locknut, i.e. the anti-loosening ratio and axial force ratio, in a more realistic manner. The connection joint of the locknut was subjected to cyclic transverse impact and the anti-loosening property was measured after a specified number of cycles. The loading effect on the surface roughness of thread surface was examined and discussed after the test. It was found that the factor of locknut type dominated the influence over the lubrication grease and fit clearance factors. Through the analysis, the design with optimal combination of the control factors improved the axial force ratio and anti-loosening ratio by 7.8% and 47.9%, respectively.

(1) Background: Primary stability—one fundamental criterion for the success of dental implants—is influenced by implant geometry even if the effect of apical shape modifications on implant primary stability has not yet been examined. Therefore, the aim of the ex vivo study was to compare primary stability of implants differing in apically located screw threads (J-line) or a flat tip (K-line) only. (2) Methods: 28 implants of each group of the same diameter (4.3 mm) were randomly inserted into porcine bone blocks. The first group (9, 11 and 13 mm) was inserted into “hard”, the second (11 mm) into “soft” bone, here using a normal and an undersized drilling protocol. Insertion torque (Ncm), Periotest® value, resonance frequency (implant stability coefficient, ISQ) and push-out force (N) were measured. (3) Results: In “hard” bone, primary stability increased with increasing length in both groups but it was significantly higher in J-line (p < 0.03). An undersized preparation of the implant bed in “soft” bone resulted in a significant increase in primary stability in both groups. Here, J-line also showed a significantly increased primary stability when compared to equally prepared K-line (insertion torque: 37 Ncm vs. 26 Ncm; Periotest®: −6.5 vs. −4.3; push-out force: 365 N vs. 329 N; p < 0.05 each). (4) Conclusions: Primary stability is significantly higher with increasing implant length and apically located screw threads as well as with undersized drilling protocols. When preparing the implant site and subsequently selecting the implant system, modifying factors such as implant geometry (also at the tip) should be taken into account.

The transmission accuracy of the ball screw depends on the processing quality of the thread profile. Traditional detection method of thread profile is complicated and inefficient. When shooting the thread profile of the ball screw in the normal section, the camera axis must be tilted to the lead angle, and adjustment errors are easily introduced from both the front view and the top view. When shooting in the axial section, the spiral lines block each other, so the actual thread profile cannot be captured for detection. In order to solve the above problems, a thread profile detection method is proposed: the theoretical equation of the ball screw thread profile in the axial section is derived based on the theoretical thread profile in the normal section, and the theoretical equation of the thread profile projection curve in the axial section is solved based on helix analysis, and the differential equation between them is obtained; then, the theoretical correction value of the thread profile projection curve is obtained by Linear Search to find the boundary value; the actual thread profile in both axial section and normal section is finally obtained with the theoretical correction value, which can support accurate measurement and detection of the key parameters of the thread profile. Experiments show that the proposed method can effectively improve the accuracy of the ball screw thread profile detection.

In order to solve manual operation and low detection efficiency in the measurement of thread geometric error, machine vision and optical enlargement are adopted to measure the high-precision geometric error of thread. For screw thread edge image characteristics, a new method using 67.5° and 112.5° improved Sobel templates to obtain the edge of image was put forward, and we calibrated the system using self-calibration method. The geometric error measurement system of screw thread was designed. The geometric error of screw thread, such as pitch, angle and diameter of screw, were calculated by extracting the coordinates of image edge. The system can be concluded that the method of machine vision, whose linear precision is less than 10 μm, can be used to detect the comprehensive parameters of screw thread. The designed measurement system was intuitive, efficient and easy to operate. It can be used in modern manufacturing and has values in generalized application.

In the process of screw thread manufacturing, the cooling liquid or lubricating oil will adhere to the screw thread surface, which affects the vision measurement results of the screw thread parameters. To simulate the adhesion behavior of oil on the thread surface during the actual measurement, four different attachment states were set in this experiment. An image measuring instrument was used to collect the screw thread images of different adhesion states. Then, the distribution of the oil film on the screw thread surface was analyzed with computer image processing. The visual inspection method was used to obtain the relative influence rate of the oil adhesion on the measurement result of the screw thread parameters. Finally, an experiment-based pitch diameter compensation method was proposed, and the compensation effect of this method was verified with the test method. Experiments showed that the effect of oil adhesion on the measurement results of the diameter parameters is greater than 7 µm, and the effect on the measurement result of the thread angle is greater than 0.1°. The compensation experiment showed that the compensation efficiency was above 70% for the pitch diameter.

This research focuses on process design of the adjustment of movable thread plate and fixed thread plate in the screw rolling machine during production. By observing some key dimensions of the threaded screw, one can determine the movement amount and the rotation direction of the adjustment screw bars mechanism of the fixed thread plate that required for the specified size of this type of screw. One establishes a relationship from the adjustment of the screw bars mechanism to the fixed thread plate posture. It can be seen that the formed screw size deviations will lead the machine operator to adopt one of the proposed process to achieve the posture adjustment of the fixed thread plate. While the screw specification deviations do not conform to the standard ones, the operator just need to find out the error type of the formed screw and measures its specification to follow one of the proposed formulas, then the wrong thread plate posture can be modified to the correct posture under operator’s adjustment. The method addressed in this research can not only reduce the operational difficulty of screw thread rolling machine but also can reduce the trial-and-error processes in traditional operation methods.

Most spine implant devices are fabricated outside Japan, and therefore do not always fit the bodies of Japanese people. This causes a quality-of-life (QOL) problem in which patients feel the embedded implant devices on their back. The aim of this study was to develop more compact and lower-profile spine implant devices. Three types of devices with different heights and different screw threads were created, and the removal torque (fitting force) of the devices was measured after a static load test and cyclic load test. In addition, the screw thread surface was observed in detail after the tests. The results indicated that the mechanism of the reduction in the fitting force was related to partial contact due to abrasion or plastic deformation of the screw thread surface and decrease in the contact area between the screw threads caused by the increased diameter of the upper opening of the implant device after tightening. Therefore, we concluded that lowering the height of the implant device, securing the number of the screw threads, and securing the contact area of the threads are important in developing a low-profile spine implant.

In order to solve the problem that the assembly axial clearance of large-diameter mechanical trigger fuze delay device is large in the fuze body, a tolerance precision control method based on the internal and external double-layer pressure screw limits is proposed. The internal and external double-layer screw threads constitute two sets of independent redundant dimensional chains in distribution direction and value. The final assembly accuracy of the delay device is adjusted by the internal and external double-layer pressure screw mutually. The minimum coaxiality deviation of assembly can achieve 0 deviation, and the average accuracy of assembly coaxiality is increased by about 30.69%, which has obvious effect in reducing axis eccentricity.

Screw loosening remains a serious complication for patients undergoing pedicle screw fixation surgeries. An accurate risk prediction is significant for prevention of screw loosening through preoperative planning. In this study, we proposed a novel index, namely the bone mineral density surrounding the screw thread (thread BMD), and tested its predictability in screw loosening. 86 screws (18 loosening and 68 non-loosening) from L3–L5 of 20 patients who experienced pedicle screw loosening were analyzed. The preoperative and postoperative quantitative CT scans of the same vertebra were spatially registered and a helix-based approach was developed to extract the thread BMD. BMDs of the vertebral body, the pedicle and the screw trajectory were also measured from the preoperative CT scans. Finite element analysis was conducted to determine pullout strength and tissue failure around the screw. Receiver operating characteristic (ROC) curve analysis was used to assess the performances of all BMD indices and pullout strength in predicting screw loosening. Linear regression was used to examine correlations between different BMD indices and screw pullout strength. The thread BMD had the greatest value of area under the curve (AUC = 0.73, p = 0.004) compared to vertebral BMD (AUC = 0.51, p = 0.923), pedicle BMD (AUC = 0.56, p = 0.474) and trajectory BMD (AUC = 0.67, p = 0.020). Also, the thread BMD showed a stronger correlation with the pullout strength (r = 0.83, p < 0.001) than vertebral BMD (r = 0.59, p < 0.001), pedicle BMD (r = 0.65, p < 0.001) and trajectory BMD (r = 0.60, p < 0.001). We developed a novel approach to measure a newly-defined thread BMD, which indicates superior capacities over other BMD indices in predicting pedicle screw loosening.

Measurements and inspection in production must be rapid, robust and automated. In this paper a new method is proposed to automatically detect screw threads in 3D density fields obtained from computed tomography measurement devices. The described method can be used to automate many operations during screw thread inspection process and drastically reduce operator’s influence on the measurement process resulting in lower measurement times and increased repeatability.